<!DOCTYPE html>
<html>
    <head>
        <meta charset='utf-8' />
        <style>
        div{
            width:200px;
            height:200px;
            display:inline-block;
            border:7px solid green;
        }
        
        div.c1{
            
        }
        div.c2{ border-radius:30px;}
        div.c3{ border-radius:20px 40px 60px 80px;background-color:yellow;}
        div.c4{ border-radius:100%;width:200px;height:200px;}
        div.c5{ border-radius:100px/200px 0px 0px 0px}   /* 1/4圆 */
        div.c6{ border-radius:100px 100px 0px 0px;height:100px;}  /*半圆*/
        </style>
    </head>
    <body>
        <div class='c1'></div>
        <div class='c2'></div>
        <div class='c3'></div>
        <div class='c4'></div>
        <div class='c5'></div>
        <div class='c6'></div>
    </body>
</html>